Method for improving fiberboard mat moldability

#This invention relates to apparatus and methods for processing fiberboard mats to condition them for molding into three dimensional objects of improved quality. More particularly, this invention provides apparatus and methods by which fiberboard mats can be incised on both upper and lower surfaces in a one pass or one direction feeding operation which loosens the mats by disrupting the fiber network, makes them pliable and leaves them with little memory so that during molding the fibers can be displaced and smoothly directed into the mold sections during hot pressing.

#The manufacture of rigid hardboard sheets generally involves compressing fiberboard mats with heat and pressure and the inclusion of one or more adhesives or binders. This process involves no particular problems when flat uniformly thick planar hardboard sheets are produced. However, the production of three dimensional non-planar hardboard panels, especially door facings, from fiberboard mats by matched die set molding causes stretch marks and fractures in deeply molded areas or regions adjacent thereto. In a molding press, the tension and compression applied to the mat by the die set pull and push the fibers of an internally self-supporting fiberboard mat apart, sometimes to the breaking point. This is a particularly significant problem with fiberboard mats which have little or no resinous binders which would flow in response to said forces to fill the space around the contours and angles of the die set to which the relatively inelastic fibers could not flow.

#The described problem is particularly troublesome when the fiberboard mat used in the molding process is produced by the water felted process. The resulting mat, which contains a minimum amount of a binder or resin, is sufficiently stiff or semi-rigid, due to its integral strength, as to be substantially self-supporting thereby permitting it to be handled manually without a separate support. However, the inherent stiffness or semi-rigidity of the mat prevents the production of high quality non-planar hardboard from such a mat by die set molding. A need accordingly exists for apparatus and methods which can be used to condition such mats, as well as mats made by other than the water-felted method, so that they can be used in die set molding to yield high quality hardboard three dimensional panels.

#FIG. 1 is an isometric drawing showing an arrangement of two pair of incision making rollers containing blades or cutters and one pair of smooth surface rollers useful in a machine for making incisions in a fiberboard mat according to the invention;

#FIG. 2 is an isometric view of an incision making roller shown in FIG. 1 in which the blades are arranged in a cross machine direction (CMD) of travel of the fiberboard mat;

#FIG. 3 is a partial side elevation of the incision making roller illustrated in FIG. 2;

#To the extent it is reasonable and practical the same or similar elements appearing in the various drawing figures will be identified by the same numbers.

#The apparatus or machine 30 shown schematically in FIG. 1 constitutes a relatively simple embodiment of the invention and solely for purposes of clarity a means to drive the rollers is not illustrated. The apparatus 30 includes a first pair 32 of incisor rollers which includes an upper incisor roller 34 and a lower incisor roller 36. The rollers 34, 36 are essentially identical in size and shape. They are positioned parallel to one another with the upper incisor roller 34 positioned vertically above the lower incisor roller 36 a slight distance so as to provide a gap or nip 38 between the rollers. The gap 38 will generally be about 0.25 to 0.375 inch when a fiberboard mat 25 having a nominal thickness of 0.75 inch is to be conditioned for molding. The gap in this regard is measured as the distance between the tips of the incisor blades of the two rollers making up the pair.

#A second pair 42 of incisor rollers constituting an upper incisor roller 44 and a lower incisor roller 46 is positioned downstream of the first pair of incisor rollers 32. The incisor rollers 44, 46 are positioned parallel to one another with the upper incisor roller 44 positioned vertically above the lower incisor roller 46 a slight distance so as to provide a gap or nip 48 between the rollers. This gap can also be about 0.25 to 0.375 inch. However, the gap 48 is desirably located about 0.5 to 1 inch above the gap 38 between the first pair of rollers so as to cause the fiberboard mat to travel a sinuous path as it passes between the first and second pair of rollers. This causes the mat to flex and the mat 25 fibers to be slightly released or loosened.